Direct vascular administration of medicaments and nutritional fluids has become the preferred mode of treatment for substantially all critically ill patients, as well as for numerous patients with chronic conditions. Indwelling intravenous (and occasionally, intra-arterial) catheters have for the most part replaced rigid needles as the preferred vehicle for vascular fluid administration. Catheter markets are generally held to be expanding rapidly, indicating general acceptance through the worldwide medical community; improvements in catheter structure and operation further permit utilization for still further medical applications.
Conventionally, such catheters include an assembly in which a flexible tube, for example of polymeric construction, is bonded to a hub, and the assembly is carried about a removable cannula which extends slightly beyond the extremity of the tube. The catheter is set in place by easing the assembly into the flesh of the patient until it just penetrates the vascular wall. When the device is so set, the cannula is removed, leaving the catheter tube indwelling. Fluid administration sets, pumps, or the like are coupled to the hub, and suitable medicinal or nutritional fluids are delivered to the patient directly into the blood.
Probably the most accepted objective method for determining the proper placement of a catheter is the occurrence of "flashback", or backflow of blood up through the catheter, in some cases into a visible reservoir in the catheter hub. Of course, since the catheter insertion process is often quite swift, it is desirable that the flashback response time be very brief, thereby to give the treating physician or nurse a fast, essentially "real time" indication of the actual position of the catheter tip. Clearly, if the flashback response time is unduly slow, the flashback function will at best be of no use to the treating physician or nurse, and at worst will be totally misleading. For example, it is desirable that the flashback function occur quickly enough to avoid cannula penetration through the back wall of the vasculature and into surrounding tissue. Likewise, it is most desirable to have a flashback acceleration scheme which may be safely used in very low blood pressure situations, such as cardiac arrest or tourniquet applications.
It is a primary object of the present invention to provide apparatus for accelerating the flashback response time in intravascular catheters.
One method, to which the principles of the present invention ultimately relate, for accelerating flashback response time, is to create a slight vacuum in a flashback chamber within the catheter hub, thereby to accelerate the flow of blood back through the cannula for indication of proper placement. Often, this is done by means of a syringe, which is coupled to the catheter, and which creates a negative pressure differential as the plunger is withdrawn. Of course, in creating the partial vacuum, it is necessary to insure that air emboli or the like are not forced through the catheter and into the vascular system of the patient. It is likewise important that the partial vacuum be as slight as possible while being effective, lest vascular collapse or tissue withdrawal be accidently caused.
It is accordingly a further object of the present invention to provide a device for accelerated flashback response time safely utilizing the vacuum pull method, while avoiding the risk of unintentional deposit of fluid, air, or the like undesirable foreign substances into the blood stream.